With the development of information society in recent years, voice and video have progressed in the level of resolution and the volume of data traffic in the Internet has also increased significantly. This in turn has resulted in an increase in electronic data volume accumulated in servers and the like, making it necessary to expand the capacity of information recording systems. Optical disc drives and hard disk drives installed as information recording devices in personal computers, recorders and cameras are being called upon to have higher recording densities to accumulate huge volumes of information. The higher recording density represents a further miniaturization of a recording bit size in the disks.
To realize an increased recording density of hard disks requires narrowing a distance between the recording medium and a head and miniaturizing the diameters of crystal grains of a magnetic film on the magnetic recording medium. The magnetic recording medium has a problem of heat fluctuation in which as the crystal grains are miniaturized in diameter, the grains become thermally unstable. This problem has come to be known in recent years as a major inhibiting factor for higher recording density. For realizing both the miniaturized crystal grains and the heat stability at the same time, it is effective to increase a coercive force. The increased coercive force in turn requires increasing the magnetic field strength of the head in performing the recording. However, since there is a limit to the property of a magnetic material used in the recording head and to the reduction in the distance between the magnetic disk and the head, it is difficult to increase the coercive force as the recording density is enhanced. To solve this problem, a optical-magnetic hybrid recording technique has been proposed that combines the optical recording and the magnetic recording. The coercive force of a medium is reduced during recording by heating the medium at the same time that an applied magnetic field is generated. This makes it possible to easily record a medium even with a high coercive force which it has been difficult for the conventional magnetic head to record because of an insufficient recording magnetic field strength. A playback operation utilizes a magnetoresistive effect that has been used in the conventional magnetic recording. This hybrid recording method is called a thermally assisted magnetic recording. Here, as a heating method based on light, a method using a near field is proposed. The thermally assisted magnetic recording based on the near field introduces a laser beam from a laser beam source and changes a beam spot diameter to an appropriate size for recording by using a device having a function to generate a near field light (hereinafter referred to as a near field light generating device) before using the spot for recording.
For the laser beam source, a small, low power consumption semiconductor laser (also referred to as a laser diode) is normally used because it must be used in a package of a disc drive. For applications in a thermally assisted magnetic recording drive using a near field that realizes a recording density of more than Tb/in2 (terabytes/square inch), a power of around several mW is required for the light beam to reach the recording medium surface.
Optical parts that introduce a laser beam generated by the laser diode (hereinafter referred to as an LD) to the near field generating device include a reflection mirror, a lens and an optical waveguide. The beam from the LD passes through optical parts installed in a light path to arrive at the near field generating device and a recording medium beyond it. The light intensity of the beam, as it passes through the light path, becomes several tens of times smaller than its original light power produced by the LD. Major causes for the light intensity attenuation include absorption loss and scattering loss that occur as the beam passes through the optical parts, and a connection loss resulting from deviations of optical parts from their ideal positions when they are bonded together. So, in the thermally assisted magnetic recording, it is essential to achieve a construction that reduces the connection loss up to the beam entering the near field generating device.
A slider in the hard disk drives, on the other hand, has progressed in quest of its size reduction from a picoslider to a femtoslider. The air bearing surface has been lowered down to a floating distance of about 10 nm. As the miniaturization advances further, the floating distance is expected to be reduced. However, as the miniaturization and the floating distance reduction make a progress, a warping of the slider itself poses a problem. For this reason, a construction needs to be developed which suppresses the warping of the slider and at the same time reduces the connection loss described above.
JP-A-2002-298302 (hereinafter referred to as a patent document 1) provides an optically assisted magnetic recording head that achieves a reduced noise in medium, the securing of a thermal agitation resistance and the recording by a practical recording head, in a construction that has an optical fiber arranged over the slider formed with a groove and introduces a laser beam through an optical prism at the end face of the slider into a near field probe and a write head, a paired structure facing the optical fiber with a gap in between. In JP-A2006-185548 (referred to as a patent document 2) a thermally assisted magnetic recording head is provided in which a slider, magnetic poles, a magnetic recording device, a magnetic playback device, a light waveguide and an opening are provided beneath a suspension, with a laser diode arranged on the opposite side of the suspension, to reduce the size and weight of the recording head. The patent document 2 also describes a construction in which the waveguide and the LD element are longitudinally arrayed in the same direction as the slider. JP-A-2007-95167 (referred to as a patent document 3) provides a thermally assisted magnetic recording head in which a semiconductor laser, a waveguide, a near field generating device and a diffractive device that functions as a slider are arranged on a suspension so that a laser beam propagates through the waveguide and is gathered by the diffractive device to illuminate a plasmon probe, thus achieving a reduced thickness with a simple construction.